I also have this problem.
The Weaver theme gives an option to "switch off" a page to appear in the menu, and to become a dead-page (dead main menu option) where only underlying pages are active in the dropdown menu.
This is from the theme support forum:
For a page checked as: Menu "Placeholder" page in the Theme (great feature that I need), the sitemap has an entry with only: #
And that is regarded invalid sitemap-syntax.
Is there anything I can do in the Theme or page or would this be a sitemap-generator bug ?
To temporarily solve this I switch the theme-option off again but for sure I would like to use that feature.